Recent studies show that young children can be highly exposed to pesticides due to their normal oral exploration of their environment and their level of dermal contact with floors and other surfaces. Farmworker children may be exposed to even higher pesticide levels as a result of pesticides tracked into their homes by farmworker household members, by pesticide drift, by breast milk from their farmworker mother, and by playing in the fields. The purpose of this proposal is to better characterize the magnitude and pathways of pesticide exposure to young children. The four specific aims are: (1) to measure prenatal and postnatal organophosphate pesticide exposure to farmworker children and to characterize population-level correlates of exposure; (2) to characterize pesticide concentrations in environmental media along exposure pathways that link children to pesticide use; (3) to describe the exposure-prone behavior of young children; and (4) to develop a multimedia multi-pathway pesticide exposure-assessment model. To meet specific aim 1, we will measure the level of organophosphates (OP) metabolites in the urine of 550 mothers during pregnancy and in the urine of their children at 6, 12, 24 and 26 months and computer descriptive statistics for the OP metabolites levels by population characteristics, e.g. season, age, parental occupation, etc. To meet aim 2, we will select from the 550 children 52 each at ages 6 and 24 months. We will administer a detailed exposure questionnaire and make measurements of OP levels in house-dust, food/beverage, parents' work clothing, hand-wipes, and maternal urine (for breast-feeding 6 month olds). To meet specific aim 3, we will select from the 52 children 10 each at ages 6 and 24 months to conduct a video-taped time-activity analysis of dermal contact and hand-to-mouth behaviors. Video-taped activities will be translated into computer text files to develop statistical descriptions of exposure-prone behavior. To meet specific aim 4, we will adapt an existing multimedia-model to the study population and region to simulate exposures for farmworker children. This model will be re-calibrated using actual exposure pathway data (from specific aim 2) and exposure-prone behavior data (from specific aim 3) to increase the reliability with which we can identify for this and other populations important exposure routes, behaviors, and pathways for children's exposures to pesticides. The ultimate goal of this research is to identify the most important exposure pathways for young children so that effective and age-appropriate interventions and policies can be designed.